A removable coupling device, of the type discussed here, comprises a boss member having a hole axially extending inwards and radially extending apertures opening in the hole. A shaft having a set groove circumferentially extending in an outer surface thereof is fitted into the hole of the boss member. Radially movable locking elements are disposed within the respective apertures such that the locking elements can be located at one of a locked position where the locking elements can partly extend inwards from the apertures so as to engage with the set groove of the shaft and can also be located at a connectable and disconnectable position where the locking elements are disengaged from the set groove. An axially movable set ring is disposed on the boss member. The set ring is axially urged by spring force so as to normally keep the locking elements at the locked position.
Coupling devices of the type described above have an advantage in that, when the shaft is inserted into the boss member, the shaft can be automatically kept at the locked position if the boss member is moved together with the joint yoke while trying to insert the shaft into the hole of the boss member under the condition that the set ring on the boss member is held by hand and moved in the direction opposite to the direction of insertion. An additional advantage is that, when the boss member is removed from the shaft, the boss member can be removed from the shaft similarly only by moving the boss member axially so as to separate it from the shaft under the condition that the set ring is held by hand and moved in the same direction as the direction of removal of the boss member. Accordingly, for example, in the case where the device of this type is used at an output shaft of a tractor for driving an agricultural machine to be connected to the tractor, the device is useful for connecting the output shaft of the tractor to a boss member having a universal joint yoke connected to the agricultural machine. On the other hand, in the case where a tractor merely pulls a car or the like, a shaft of the tractor can be removably connected to a shaft of the car. Furthermore, the device can be used for speedily connecting and disconnecting pipes, such as fire hoses or the like.
Although shafts for transmitting rotational motive power are used in various kinds of machines, the shafts are difficult to handle in connecting and disconnecting operations and often cause danger because the joint portion thereof is generally disposed at a narrow portion and/or because covers are provided to prevent stain. Furthermore, speedy connection and disconnection should be required for fire hoses or the like. In order to solve such problems, various kinds of devices for safely, securely and speedily performing the connection of the shafts have been proposed. Among those proposals, such a coupling device as described above in the introduction, in which the connection and disconnection is connection of the shaft can be easily made by axially moving the set ring when the shaft is inserted into or removed from the boss member, has been proposed in the specification and drawings initially appended to the request of an application of each of Japanese Patent Unexamined Publication Nos. 41017/1986, 52420/1986 and 84410/1986 and Japanese Patent Application No. 118949/1985 (corresponding to U.S. patent application Ser. No. 779,268 filed Sept. 23, 1985) now U.S. Pat. No. 4,645,372.
However, those proposed devices are disadvantageous in the following points. Many parts are required. The structure is complex. A long time is required for assembling the coupling device. Particularly, almost of those devices are disadvantageous in that it is necessary to search the current position of the shaft by feeling while holding the set ring by both hands and moving the set ring frontwards. It is also necessary to move the boss member together with the universal joint to push the boss member against the shaft so as to insert the shaft into the hole of the boss member. Accordingly, the proposed devices are difficult to handle in connecting and disconnecting operations and are not fully satisfactory, and improvement thereof has been expected.